The present invention relates in general to a switching method, switching equipment and a switching network, and more particularly to switching of cells which are transferred with an ATM (Asynchronous Transfer Mode) and a switching network.
As a switching method in a public network, at the present time, the STM (Synchronous Transfer Mode) is employed. In the STM, the switching processing is executed in time slots within a frame. As an example of such a frame structure, there is known a frame structure in which in a DS1 transferred at a signal rate of 1.544 Mbits/sec, a set of 193 bits is treated as one frame, the first bit is the bit which is used to carry out the frame synchronization and the like and with respect to the bits from the second bit on, 8 bits are treated as 1 channel (time slot) so that 24 channels are assigned. The existing STM network executes the switching processing in channels. On the other hand, in the ATM, for a ATM cell of 53 bytes consisting of a header part of 5 bytes and an information part (payload) of 48 bytes, the switching processing is executed in ATM cells on the basis of the information contained in the header.
In general, in the ATM and the like, it is conceivable that the various media such as voice and data are handled. Since the character is different between the voice and the data, the processing layer for converting the respective media signals into the ATM signals, i.e., an AAL (ATM Adaptation Layer) is defined in the ITU-T I. 363 series. For example, when converting the existing STM signal into the ATM signal, an AAL type 1 is used, when transferring the encoded voice data, an AAL type 2 is used, an AAL type 5 is used for the variable length packet data, and so forth.
Now, the description will hereinbelow be given with respect to the delay when transferring the information relating to voice or the data. In the case where one ATM connection is simply given to one channel of the STM signal, since when generating one ATM cell, the ordering of the ATM cell is waited until data for 48 bytes has been well arranged, the delay will occur. More specifically, in order that one ATM cell may be generated with the signals of only one channel at a signal rate of 64 kbits/sec, it takes about 6 msec with 125 xcexcsecxc3x9748 frames (bytes). Therefore, as the method of shortening a time to generate the ATM cell when converting the existing STM signal into the ATM signal, there is known the method of assigning a plurality of channels in the STM to one ATM connection. This method is defined as the Structured Data Transfer Method of the AAL type 1 in ITU-T I. 363.1. When adopting this method, if for example, one ATM cell is generated with signals of 24 channels at a signal rate of 64 kbits/sec, then the ATM is generated for a time of about 0.25 msec (125 xcexcsecxc3x9724 channelsxc3x972 frames), and hence the delay in generation of the ATM cell can be reduced. Similarly, in order to reduce the delay when transferring the encoded voice data packet, the method wherein the CPS (Common Part Sublayer) packets to which the CIDs (Channel Identifiers) used to identify the channels are added are multiplexed in one ATM connection is to be transferred is defined in the AAL type 2 in ITU-T I. 363. 2.
Next, the description will hereinbelow be given with respect to the method of identifying the channels when signals of a plurality of channels are multiplexed in the ATM cells as described above. In the Structured Data Transfer Method of the AAL type 1, the variable length block is generated with signals of a plurality of channels which are handled in the STM signals and the resultant block is transferred through one ATM connection. In accordance with this Structured Data Transfer Method, since the transfer is carried out with the offset signal exhibiting the location of the boundary between the blocks contained within the payload of the ATM cell, the block can be generated on the reception side by utilizing that offset signal. In this connection, into which location within the block which channel is inserted is predetermined between the offices, whereby the respective channels can be identified on the reception side.
In addition, in the AAL type 2, since the CID is added each of the CPS packets, the channels of the CPS packets can be identified on the basis thereof.
In the conventional Structured Data Transfer Method of the AAL type 1, as described above, a plurality of channels are assigned to one ATM connection. For this reason, the signals of a plurality of channels are necessarily transferred to the same destination. On the other hand, if the ATM connections are assigned to the respective units to which the signals of a plurality of the channels are to be transferred, then there arises the problem that the delay will be increased as described above. This is also applied to the AAL type 2 with which the encoded voice data is transferred. As for the method of reducing the delay time, for example, there is known a partially filled cell method which is shown in ITU-T I. 363. 1. This method is such that the user information is contained in a part of the ATM cell and the dummy fill is contained in the remaining part. In the case of this method, however, since the meaningless signal is necessarily contained in the ATM cell, the number of cells in the switching equipment or the network is increased. This exerts an influence on the traffic characteristics. In order to solve this problem, the internal signal transfer speed needs to be increased. This is not economical.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art. It is therefore an object of the present invention to provide a network, switching equipment and a switching system by which when signals of a plurality of channels are transferred in the form of the ATM cells, the signals can be transferred economically and with small delay, and in addition thereto, the unit to which the signals are to be transferred can be selected every channel.
It is another object of the present invention to provide a technology by which when a voice data signal decode circuit is provided in a network, an encoded or decoded voice data signal can be transferred economically and with small delay and also the unit to which the signals are to be transferred can be selected for channels having different destinations.
It is still another object of the present invention to provide a technology by which since when signals of a plurality of channels which have been multiplexed by the Structured Data Transfer Method of the AAL type 1 or signals of a plurality of channels which have been multiplexed the AAL type 2 are intended to be transferred, those signals are transferred with those signals multiplexed, the transfer can be carried out economically and with small transfer delay, and the unit to which the signals are to be transferred can be selected every channel in a network and also the multiplexing can be made in the ATM cell every unit to which the signals are to be transferred.
It is yet another object of the present invention to provide switching equipment, a switching system and a network in which in a network in which cells subjected to the ordering of the ATM cells by utilizing a plurality kinds of AALs, the conversion of the AAL type, the conversion of the signals or the like (encoding, decoding, encryption or the like of codes) is carried out in such a way as to be able to interconnect those systems, so that information which has been contained in the ATM cell is transferred to a desired destination.
In order to solve the above-mentioned problems associated with the prior art, according to an aspect of the present invention, there is provided a network having a function of inputting first ATM cells which have been generated by multiplexing signals of a plurality of channels to switch signals of the plurality of the channels which are multiplexed in the plurality of first ATM cells to generate second ATM cells to output the second ATM cells thus generated. In addition, according to another aspect of the present invention, there is provided a network wherein the first ATM cells or the second ATM cells are each the ATM cells which are generated by the Structured Data Transfer Method of the AAL type 1 or the AAL type 2, or the ATM cells which are generated by an AAL type 5.
According to a first solution of the present invention, there is provided a switching method including the steps of:
inputting ATM cells of a first type which have been generated by multiplexing signals of a plurality of channels; and
switching said signals of the plurality of the channels which are multiplexed in the plurality of ATM cells of the first type and converting the signals of the channels to the same destination into ATM cells of a second type which are employed by the same destination to output the ATM cells of the second type thus obtained.
According to a second solution of the present invention, there is provided a switching method including the steps of:
inputting ATM cells of a first type and ATM cells of a second type which have been generated by multiplexing signals of a plurality of channels having different destinations; and
switching the signals of the plurality of the channels which are multiplexed in the plurality of ATM cells of the first type and the plurality of ATM cells of the second type, and converting the signals of the channels to the same destination into the ATM cells of the first type, the ATM cells of the second type or ATM cells of another type which are employed by the same destination to output the resultant ATM cells.
According to a third solution of the present invention, there is provided switching equipment including:
an ATM switch for accommodating therein a plurality of ATM lines to carry out switching with header information of ATM cells; and
an ATM upper layer switch having an input and an output connected to the ATM switch for inputting ATM cells of a first type which have been generated by multiplexing signals of a plurality of channels and switching the signals of the plurality of the channels which are multiplexed in the plurality of ATM cells of the first type to generate ATM cells of a second type to output the ATM cells of the second type thus generated to the ATM switch.
According to a fourth solution of the present invention, there is provided switching equipment including:
a first ATM upper layer switch for accommodating therein a plurality of ATM lines and inputting ATM cells of a first type which have been generated by multiplexing signals of a plurality of channels and switching the signals of the plurality of the channels which are multiplexed in the plurality of ATM cells of the first type to output the resultant signals;
an ATM cell switch connected to the first ATM upper layer switch for carrying out switching with header information of the ATM cells; and
a second ATM upper layer switch having an input and an output connected to the ATM cell switch for inputting the ATM cells of the first type which have been generated by multiplexing signals of the plurality of the channels and switching the signals of the plurality of the channels which are multiplexed in the plurality of ATM cells of the first type to generate ATM cells of a second type to output the ATM cells of the second type thus generated.
According to a fifth solution of the present invention, there is provided a switching network including a plurality of switching equipment as described above, wherein a source which will employs ATM cells of a first type inputs the ATM cells of the first type which have been generated by multiplexing signals of a plurality of channels; the signals of the plurality of the channels are switched which are multiplexed in the plurality of ATM cells of the first type, and the signals of the channels to the same destination are converted into ATM cells of a second type which are employed by the same destination to be outputted; and the same destination receives the ATM cells of the second type.
Other objects, features and advantages of the present invention will become apparent from the description of the embodiments of the invention taken in conjunction with the accompanying drawings.